I guess her feet/hooves are so used to being in heels, they automatically go into that position when she's standing. Twat.

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Or she's trying to minimize the horror of their size. One hoof is completely hidden and the other is in a vertical position. When the foot/leg is in the "L" position, or flat, it emphasizes the size of the foot; when it's up, it looks more like just an extension of the leg.